Melt spinning process

ABSTRACT

The ability to maintain a constant differential between modification ratios of trilobal filaments under cospinning conditions is provided by spinning a filament of lower modification ratio through a spinneret orifice consisting of three radially intersecting tapered slots and a filament of a higher modification ratio through a spinneret orifice configured as three radially intersecting reverse-tapered slots. The orifices configured as three radially reverse-tapered slots provide a high modification ratio with low sensitivity to normal spinning process fluctuations which in combination with orifices having tapered slots for filaments of lower modification ratio facilitate maintenance of a more constant differential in modification ratios between the filaments.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for cospinning synthetic trilobalfilaments differing in modification ratios. More particularly, thefilaments are cospun from trilobal spinneret orifices of differentconfigurations.

2. Description of the Prior Art

Synthetic filaments having trilobal cross-sections and particularbenefits associated therewith are described, for example, in U.S. Pat.No. 2,939,201. A characteristic of such filaments is their cross-sectionmodification ratio, or MR. Certain benefits can be obtained frommixtures of such filaments or fibers having different modificationratios as described, for example, in U.S. Pat. No. 3,220,173. Aconvenient method of preparing such filament mixtures is to co-spin thedifferent types in the desired ratio and to process the combinedfilaments through subsequent steps such as drawing, crimping, cuttinginto staple, etc. as a single mixed-filament product.

When filaments of two different modification ratios are co-spun usingtwo differently dimensioned sets of known capillaries such as those withthree intersecting slots with each having parallel sides, randomfluctuations in process variables such as spinning temperature cause MRchanges along and among filaments. Process adjustments to maintain anacceptable difference in MR between the two filament species is quitedifficult.

An object of this invention is to reduce the sensitivity to normalspinning process fluctuations of changes in the difference inmodification ratios among filaments cospun from a common polymer supplythrough at least two spinning capillaries designed to yield differentfilament modification ratios and where one of the modification ratios isgreater than 1.9.

SUMMARY OF THE INVENTION

The invention is an improvement in a process for cospinning at least twosynthetic trilobal filaments from the same polymer melt wherein onefilament has a modification ratio no greater than 1.9, the otherfilament has a modification ratio greater than 1.9, and the twofilaments differ in their modification ratios by at least 0.3 andpreferably by at least 0.6 MR units. The improvement comprises spinningthe filament of lower modification ratio through a spinneret capillaryconfigured as three radially intersecting tapered slots and spinning thefilament of higher modification ratio through a spinneret capillaryconfigured as three radially intersecting reverse-tapered slots.

Preferably the tapered and reverse-tapered slots are tapered to definean angle of from about 3° to about 15° between intersecting imaginarylines which are extensions of the sides of a given slot.

DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the magnified transverse cross-section of a spinneretcapillary comprised of three radially intersecting tapered slots.

FIG. 2 represents the magnified transverse cross-section of a spinneretcapillary comprised of three radially intersecting reverse-taperedslots.

In FIG. 1, symmetrical capillary 20 consists of three radiallyintersecting slots 22 whose imaginary center lines 23 intersect atcenter point 24. Each slot 22 has the same length 25 measured betweencenter point 24 and flat tip 28 which is perpendicular to center line23. Each slot 22 is tapered such that the base width 26 is greater thanthe width of tip 28 to define a taper angle B between imaginaryextensions 29 of the sides of slot 22. Angle C between adjacent slots 22is shown equal in each instance (120°).

In FIG. 2, symmetrical capillary 30 consists of three radiallyintersecting slots 32 whose imaginary center lines 33 intersect atcenter point 34. Each slot 32 has the same length 35 measured betweencenter point 34 and flat tip 37 which is perpendicular to center line33. Each slot 32 is reverse-tapered such that the base width 36 is lessthan width 38 of tip 37 to define a taper angle D between imaginaryextensions 39 of the sides of slot 32. Angle E between adjacent slots 32is shown equal in each instance (120°).

Although the capillaries of the Figures are shown to be symmetrical ineach instance, symmetry is not a requirement of this invention providedthe specific shape conditions are met. For example, lengths 25 or 35 andangles C or E may differ among slots in the same capillary. The slottips of all three capillary types may be squared, rounded, expanded, orotherwise modified as known in the art without changing their relativeperformances as described herein.

DESCRIPTION OF THE INVENTION

Spinneret capillaries for spinning trilobal filaments configured asthree radially intersecting slots which radiate from a common point arewell-known. The modification ratios of filaments spun from suchcapillaries are affected not only by configuration and size of thecapillary but also by spinning conditions such as polymer relativeviscosity, spinning temperature, and quenching conditions used forsolidifying the freshly spun filaments. When using a common polymersupply and identical spinning and quenching conditions (i.e., whencospinning) to produce filaments having a desired constant difference inmodification ratios, such fluctuations in processing conditions can havea highly undesirable effect upon the modification ratio differential.This invention facilitates maintenance of a fixed differential inmodification ratio between filaments under such normal fluctuatingconditions when one filament has a modification ratio greater than 1.9.

The process of this invention is particularly useful for cospinningfilaments in the manufacture of crimped staple fibers for use in carpetyarn wherein the filaments of one group have a modification ratio withinthe range of 1.6 to 1.9 and the filaments of another group have amodification ratio within the range of 2.2 to 2.5.

The modification ratio of filaments spun through tapered trilobalcapillaries as in FIG. 1 is relatively insensitive to changes inspinning conditions. Unfortunately, the highest modification ratiopracticably obtainable with such capillaries is only about 1.9.Therefore, the tapered slot configuration is not suitable for the highMR filaments of this invention which have an MR in excess of 1.9(preferably 2.2 to 2.5).

"Modification ratio" (MR) as used herein is defined as the ratio of theradius of a circle which circumscribes the filament cross-section to theradius of the largest circle which can be inscribed within the filamentcross-section. For filament cross-sections having substantially equallobes, these circles are concentric as described in Holland U.S. Pat.No. 2,939,201.

The MR of each filament type is determined on the as-spun filamentsprior to any cold-drawing step by measuring 10 filaments of eachparticular filament type and calculating the average. In actualpractice, the measurements are made on photographic enlargements ofcarefully microtomed cross-sections of undrawn yarn. Considering methoderror, a constant MR is assumed when none of the individual measurementsdiffer from the average by more than ± 0.15 MR units.

"Relative viscosity" (RV) is the ratio of absolute viscosities at 25° Cof a polymer solution to its solvent. In the Examples, the solvent isformic acid/water (90/10 parts by weight) and the solution is preparedby dissolving 5.5 gm. of dried polymer in 50 ml. (25° C) of the solvent.As employed herein, the "polymer" is always a sampling of freshlyextruded filaments.

The term "cospinning", as used herein, applies not only to spinning twotypes of filaments through different capillaries in the same spinneret,but also to spinning through at least two spinnerets of the samespinning machine where all capillaries of each spinneret are identicalbut differ from spinneret to spinneret. In any case, the filaments ofboth types are spun from a common polymer supply under substantiallyidentical spinning conditions and are combined to provide a mixedfilament or fiber product.

Polymers useful in the process of this invention are any of thoseconventionally melt spun. Polyamides are preferred, includingpolyhexamethylene adipamide (66 nylon), polycaproamide (6 nylon), andtheir copolymers. Polyesters (e.g., polyethylene terephthalate),copolyesters, and polyalkylene polymers (e.g, polypropylene and itscopolymers) are also advantageously employed.

In the following examples filaments are extruded from a supply ofpoly(hexamethylene adipamide) containing 0.02% by weight TiO₂delusterant as very fine dispersed particles. A screw-melter convertsthe flake polymer to polymer melt. Relative viscosity of the melt isvaried as desired by controlling temperature and relative humidity ofrecirculating inert gas in a conditioner through which flake passesbefore being melted. Nominal RV of the extruded polymer is about 66,but, as specified hereinafter, RV is varied over a range of 60 to 72 totest the effect of RV on MR. Unless otherwise specified, extrusiontemperature of the melt is 290 ± 2° C.

Filaments in each example are produced at a single position fitted witha spinneret plate having 332 extrusion capillaries arranged in 8parallel rows in staggered array such that each odd-numbered row has 42and each even-numbered row 41 capillaries. All capillaries inodd-numbered rows are identical with a given trilobal cross-section, andall capillaries in even-numbered rows are identical with a differenttrilobal cross-section. Exact cross-sections are specified hereinafter.The polymer melt is spun to filaments at the rate of 110 lb./hr. (49.9kg./hr.), and the filaments are quenched in a chimney using cross-flowair at 45 ± 3° F. (7.2 ± 7° C) and quench-air flow rates of from 290 to380 ft.³ /min. (8.21 to 10.76 m.³ /min.), as subsequently specified. Thequenched filament bundle is then collected as a tow which, in a separateoperation, is drawn at a draw-ratio of 3.75X and crimped conventionallyin a stuffer-box crimper. All filaments so prepared are nominally of 18dpf (20 dtex).

EXAMPLE I

This Example utilizes a spinneret plate having only the taperedinsensitive capillaries of FIG. 1 and consequently is not of theinvention.

The odd-numbered rows in the spinneret plate (producing the low-MRspecies) have capillaries characterized by: slot length 25 is 14.0 mils(0.36 mm.), base width 26 is 7.0 mils (0.18 mm.), width of flat tip 28is 4.3 mils (0.11 mm.), taper angle B is 12.8°, and symmetrical slotangle C is 120°. Capillary length is 4.0 mils (0.10 mm.).

The even-numbered rows (producing the high-MR species) have capillariescharacterized by: slot length 25 is 17 mils (0.43 mm.), base width 26 is7.6 mils (0.19 mm.), width of flat tip 28 is 4.8 mils (0.12 mm.), taperangle B is 3.25°, and symmetrical slot angle C is 120°. Capillary lengthis 8.0 mils (0.20 mm.).

Measured filament modification ratios under the shown spinningconditions are:

    ______________________________________                                        Low MR Values -                                                               Quench-air flow                                                                              Yarn RV          MR                                            ft. .sup.3 /min.                                                                      m..sup.3 /min.                                                                            60±3                                                                               66±3                                                                             72±3                                                                             Change                                ______________________________________                                        290      8.21      1.65    1.70  1.75   0.10                                  320      9.06      1.70    1.65  1.75   0.10                                  350      9.91      1.70    1.70  1.80   0.10                                  380     10.76      1.65    1.80  1.80   0.15                                          MR Change  0.05    0.15  0.05                                         High MR Values -                                                              Quench-air flow                                                                              Yarn RV          MR                                            ft. .sup.3 /min.                                                                      m..sup.3 /min.                                                                           60±3 66±3                                                                             72±3                                                                              Change                                ______________________________________                                        290      8.21      1.75    1.80  1.85   0.10                                  320      9.06      1.80    1.80  1.90   0.10                                  350      9.91      1.75    1.85  1.85   0.10                                  380     10.76      1.80    1.90  1.95   0.15                                          MR Change  0.05    0.10  0.10                                         ______________________________________                                    

These results show that the MR from each set of capillaries isrelatively insensitive to process variables and the differential betweensets remains relatively constant; however, the desired differential of0.3 between sets was not obtained in spite of the differences incapillary dimensions.

EXAMPLE II

This example shows cospinning two species differing in MR by at least0.3 MR units and having a high MR in excess of 1.9 and a low MR lessthan 1.9. The odd-numbered rows of the spinneret plate (producing thelow-MR component) have tapered capillaries (FIG. 1) identical to thoseof the odd-numbered rows in Example I. The even-numbered rows (producingthe high-MR component) have reverse-tapered capillaries as shown in FIG.2 and characterized by: slot length 35 is 18.3 mils (0.46 mm.), basewidth 36 is 5.7 mils (0.14 mm.), flat tip width 38 is 7.6 mils (0.19mm.), reverse taper angle D is 6.5°, and symmetrical slot angle E is120°. Capillary length is 8.0 mils (0.20 mm.).

Modification ratios obtained with changes in quench air flow and RV are:

    ______________________________________                                        Low MR Values -                                                               Quench-air flow                                                                              Yarn RV          MR                                            ft..sup.3 /min.                                                                       m..sup.3 /min.                                                                           60±3 66±3                                                                             72±3                                                                              Change                                ______________________________________                                        290      8.21      1.65    1.70  1.70   0.05                                  320      9.06      1.60    1.65  1.75   0.15                                  350      9.91      1.65    1.75  1.70   0.10                                  380     10.76      1.70    1.70  1.75   0.05                                          MR Change  0.10    0.10  0.05                                         High MR Values -                                                              Quench-air flow                                                                              Yarn RV          MR                                            ft. .sup.3 /min.                                                                      m..sup.3 /min.                                                                           60±3 66±3                                                                             72±3                                                                              Change                                ______________________________________                                        290      8.21      2.35    2.40  2.55   0.20                                  320      9.06      2.30    2.35  2.55   0.25                                  350      9.91      2.40    2.45  2.60   0.20                                  380     10.76      2.45    2.55  2.65   0.20                                          MR Change  0.15    0.20  0.10                                         ______________________________________                                    

Modification ratios obtained with changes in quench air flow andextrusion temperature are:

    ______________________________________                                        Low MR Component (RV 66±3)                                                 MR Values -                                                                   Quench-air flow                                                                              Extrusion Temperature                                                                          MR                                            ft. .sup.3 /min.                                                                     m..sup.3 /min.                                                                            287° C                                                                         291° C                                                                       295° C                                                                        Change                                ______________________________________                                        290     8.21       1.65    1.70  1.75   0.10                                  380    10.76       1.70    1.75  1.80   0.10                                         MR Change   0.05    0.05  0.05                                         High MR Component (RV 66±3)                                                MR Values -                                                                   Quench-air flow                                                                              Extrusion Temperature                                                                          MR                                            ft. .sup.3 /min.                                                                     m..sup.3 /min.                                                                            287° C                                                                         291° C                                                                       295° C                                                                        Change                                ______________________________________                                        290     8.21       2.30    2.45  2.55   0.25                                  380    10.76       2.40    2.60  2.65   0.25                                         MR Change   0.10    0.15  0.10                                         ______________________________________                                    

Comparison of the MR changes for this high-MR component with those ofthis low-MR component reveals that the reverse-tapered high MR capillaryof FIG. 2 is only slightly more sensitive to process variables, than isthe tapered capillary of FIG. 1. The ranges of RV and quench air-flowinvestigated in the example are broader than any variations normallyanticipated in a given commercial production process. Thus, using thetapered capillary of FIG. 1 for a low-MR component cospun with a high-MRcomponent utilizing the reverse-tapered capillary of FIG. 2 yields a MRdifferential which is constant within the normal accuracy of detectionof shifts in MR which affect product quality.

What is claimed is:
 1. In a process for cospinning at least twosynthetic trilobal filaments from the same polymer melt wherein onefilament has a modification ratio no greater than 1.9 and the otherfilament has a modification ratio greater than 1.9 and the two filamentsdiffer in their modification ratios by at least 0.3, the improvementcomprising spinning the filament of lower modification ratio through aspinneret orifice configured as three radially intersecting taperedslots and spinning said other filament through a spinneret orificeconfigured as three radially intersecting reverse-tapered slots.
 2. Theprocess of claim 1 wherein the tapered slots and the reverse-taperedslots have a taper angle of from about 3° to about 15°.
 3. The processof claim 2 wherein the modification ratio of the one filament is fromabout 1.6 to about 1.9 and the modification ratio of the other filamentis from about 2.2 to 2.5.
 4. The process of claim 1 wherein thedifference in modification ratio between the one filament and the otherfilament is at least 0.6.
 5. The process of claim 1 wherein the polymeris poly(hexamethylene adipamide).